As if a mere adjustment of the cut would fix anything. That's far too short-sighted and simplifies the real issue.

Customers/backlog
I'm not a dev, so of course I can only speak from the perspective of a customer. And as a customer I don't have infinite resources: My money and even more as I get older my time is limited. When I reflect on my purchasing behavior and my Steam library itself I notice: I buy way fewer games that I did year ago. Why? Limited time, as mentioned before. That limited time I want to invest in the games that interest me the most (right now) and games I see myself complete - be it a short, sophisticated game with fresh gameplay or a longer game with long-time motivations (collectibles, dense story, ...). Furthermore, I amounted a huge backlog of games that are cool but didn't get to play or finish yet.

Market saturation
What I want to say is that my library is oversaturated. Others already mentioned here in the comments: The market is oversaturated, too. Hundreds of games come out every day and not only do they have to compete with current or future games, but also loads of older (indie)games (e.g. why play a new probably average indie metroidvania when I haven't even touched masterpieces like Hollow Knight, Dead Cells, Shovel Knight or Celeste?). Of course people pay attention to Steam reviews a lot and will probably refrain from buying a game that might not be rated positive enough in their opinion.

Customer expectations
Also, customer interest is way different than years ago: Many players expect "games as a service", multiplayer/coop games and most importantly communication (even more with early access games). You can't throw your game at the store and expect the algorithm to sell it for you. Building a community and communicating with users through blog posts isn't only important on release, but before and after it. Maybe your average-looking farming sim or mediocre JRPG is just that: Not good enough. And even if it's great you have to convince people of it being great not only when they play it, but before: Sell your game. Marketing, communication, build your community.

Why I and probably many others use Steam
Even though Steam has many half-assed features (broadcasts, new chat, 32-bit client without ipv6 support, ...) it's still considered the status quo. Why? Because there is nothing better around especially on Linux:
Epic: Nothing aside from freebies or exclusives keeps customers there, because there is nothing else. Also, no Linux support
GOG: On the rise (see recently released article), but still no Linux support.
Steam: Sales, returns, community, excellent Linux support with Proton which is absolutely insane if you look just 5 years back in time, ...
Don't get me wrong. As soon as there is a really superior platform on the market or Steam turns anti-customer, people will switch and vote with their wallets. See the paid mods drama they started or that the Steam cut already gets adjusted if you reach a certain threshold sales (which is still out of the league for indie games, though).

Conclusion
What's the solution then? I don' know! I'm not getting paid to come up with one.
Is Steams cut too high? Probably, depending of how much devs use Steam features in their games. As a minimum they'll give you an audience that you have to make use of, host your game, do the billing and a lot of community features from a forum over game server network capacity to inventories with paid skins and stuff. Maybe let devs choose what they need and adjust the cut based on that.
Should the price parity be dropped? Depends. If a dev decides to release on a storefront with fewer features that can offer to sell their game cheaper due to lower running costs or whatever, that should be possible. But what would happen in the long term? I think games value and prices would drop even more, which first seems good but quality would severely suffer long-term. E.g. key stores are there yet and Steam sees nothing of the money gained there, even though they cover all hosting costs and stuff.
All in all I believe Valve is still a giant money-sink that could innovate way more. Since they are privately-owned, nobody knows how much money they really own or where it goes. Imo they haven't abused their market power that much. If other big companies like EA or Activision would be in charge, we'd be screwed. But for the time being, competition hasn't managed to catch up despite Valve's/Steam's flaws and due to the complexity of the market.